1. Technical Field
This disclosure relates generally to an organic light emitting diode (OLED) display, and more particularly, to an OLED display with improved luminance uniformity.
2. Description of Related Art
An organic light emitting diode (OLED) display is a self-emissive display in which light of desired wavelength is emitted by excitons formed by recombination of electrons and holes. Because an OLED display does not require a separate light source, for example, a backlight, some exhibit advantages including reduced power consumption, wide viewing angles, and fast response. Accordingly, OLED displays have been proposed as next generation displays. OLED displays are classified as passive matrix displays and active matrix displays. Recently, active matrix displays with low power consumption, small dot pitch, fast response, wide viewing angles, and slim form factors have been widely used.
An active matrix OLED display comprises a substrate on which a pixel area is formed. A non-pixel area surrounding the pixel area comprises data, scan, and light emission signal drivers, which drive each of the pixels. The non-pixel area further comprises a power line (ELVDD), which supplies a common voltage to the pixels, and a cathode power line (ELVSS), which supplies cathode voltages to the OLED elements. In displays for small mobile devices, the power line (ELVDD) is generally formed along one edge of the pixel or display area which reduces dead space in the display. The power line (ELVDD) typically has a uniform line width from one end of the edge to the middle of the edge. However, the power line is much narrower from the middle to the other end of the edge. The cathode power line (ELVSS) is formed adjacent to the narrow portion of the power line (ELVDD).
The change in width of the power line (ELVDD) causes a voltage drop (IR drop) in the narrower portion, which in turn causes a luminance deviation between the two portions of the display area corresponding to the wider and narrower portions of the power line. Degradation of OLED elements exposed to the higher voltages disposed proximal to a power input terminal of the power line, which are and exhibit the highest luminances.